As time goes on, integrated circuit memories require faster access times to remain commercially competitive. Integrated circuit memory cores have traditionally included MOS memory cells located at intersections of word lines and bit line pairs, typically in each of a plurality of memory blocks. Recently, integrated circuit fabrication techniques have allowed bipolar transistors to be fabricated alongside MOS transistors. An improvement in speed became possible because bipolar transistors generally switch faster than MOS transistors. One way of using the bipolar transistors is in transistor-transistor logic (TTL) circuits. TTL circuits are faster than corresponding MOS circuits and can be modified to use MOS transistors as current sources. But TTL has disadvantages. Bipolar transistors used in TTL circuits require significant amounts of base current for biasing of transistor terminals, which restricts the usefulness of TTL circuits in a low power memory. TTL circuits also require a relatively large power supply voltage. In most applications, a power supply voltage of approximately 5.0 volts is provided, but in other applications the power supply voltage is reduced to about 3.0 volts or below. TTL circuits are unable to function correctly at such a small power supply voltage.
Another way of using bipolar transistors is in emitter coupled logic (ECL) circuits. ECL circuits are faster than TTL circuits. Furthermore, they can be used with relatively-small differential signals, which can be propagated more quickly throughout the integrated circuit. However ECL circuits require more current than corresponding MOS circuits. Integrated circuit memories must meet predetermined current specifications, and the large amount of current consumed by ECL circuits also restricts their usefulness. Another constraint is that if faster ECL circuits are used, for example in decoding, a large amount of current is switched internally during a short period of time. The large amount of current creates di/dt transients on internal ground lines. If too much current is switched at the same time, a spike in the ground voltage, from the ground line inductance (L) multiplied by di/dt, may cause internal circuitry to fail.